Poly(N-vinylpyrrolidone)-Assisted Crystal Growth of Zeolitic Imidazolate Framework (ZIF-67) and Electrochemical Properties of Its Derivatives for Flexible Supercapacitors

A simple and explicit wet chemical method enables the room-temperature crystallization of the zeolitic imidazolate framework (ZIF-67) using cotton-cloth (CC) as a substrate; where time-dependent Avrami’s kinetic studies demonstrated sluggish nucleation and fast crystal growth resulting in unprecedented morphologies–truncated cubes [synthesized without poly(N-vinylpyrrolidone); PVP], and rhombic dodecahedra (with PVP) with average sizes ranging from 500 nm to 1.41 μm; wherein amphiphilic PVP plays a crucial function of structure directing agent by modulation of complex formation and deprotonation equilibria. To study the potential of pristine ZIF-67 (ZP0) and PVP-functionalized ZIF-67 (ZP50, ZP100, and ZP200) grown on the CC substrate for application as a flexible electrode in supercapacitors, ZP0, ZP50, ZP100, and ZP200 were annealed to form CZP0, CZP50, and CZP100, respectively. Areal capacitances of 181 and 214 mF·cm–2 were achieved at a current density of 1 mA·cm–2 and a potential window of 1.6 V for CZP0 and CZP100, respectively, and compared to the derivatives without PVP; CZP100 exhibited a superior energy density of 76.3 μWh·cm–2 and a capacitance retention of 84.3% after 5000 cycles at a current density of 0.5 mA·cm–2.